1. Field of the Invention
The present invention relates to an image pickup apparatus for picking up (imaging), recording, and reproducing a still image or a moving image, and relates to a control method for the image pickup apparatus.
2. Description of the Related Art
Some battery pack for a digital camera as an image pickup apparatus has a communication function. Such a battery (communication battery) is able to calculate remaining capacity information or other information based on battery voltage information, battery discharge current information, etc., and transmit the calculated information to a camera main unit via a communication line.
Aside from battery, an AC adapter can be mounted to a digital camera for use as a power source. The AC adapter converts external AC power supplied thereto via an AC power cord into DC power, and supplies the DC power to the camera. Since the AC adapter is soon unable to supply the DC power when the AC power cord is unplugged, it is preferable to notify in some way the digital camera of the unplugging of the AC power cord.
Some prior art AC adapter is configured to combine its DC output voltage with a signal voltage that varies according to DC voltage specification information, thereby notifying the DC voltage specification information to an electronic equipment supplied with the DC output voltage of the AC adapter (see, Japanese Laid-open Patent Publication No. 7-143749).
A digital camera using the above-described communication battery has a battery housing unit provided with a communication line terminal. Therefore, it may be possible to dispose an AC adapter in the battery housing unit and detect a change in DC output voltage of the AC adapter by utilizing, e.g., the technique disclosed in Japanese Laid-open Patent Publication No. 7-143749. With this conceivable arrangement, the digital camera mounted with the AC adapter is able to determine that the AC power cord is unplugged when it detects a reduction in the DC output voltage of the AC adapter (cord unplugging notification) via the communication line.
In a digital camera using two or more power supplies, however, AC power cord unplugging cannot be determined by the above-described conceivable arrangement in some cases.
It is assumed for example that a digital camera has a camera main unit and an accessory attached thereto, different power supplies are used for the camera main unit and the accessory, the accessory does not have communication means to communicate with its power source, and the camera main unit has its communication means of single system. In that case, the camera main unit manages both the power supplies, while switching the communication destination of the communication means between the power supplies for the camera main unit and the accessory. In other words, it is impossible for the camera main unit to simultaneously monitor the power supply for the camera main unit (e.g., AC adapter) and the power supply for the accessory (e.g., communication battery).
With the above arrangement, if the AC power cord of the AC adapter is unplugged when the camera main unit is communicating with the communication battery for the accessory, the camera main unit cannot detect the unplugging of the AC power cord. If some data is being written into a memory card at the instant that the power cord is unplugged, there is a fear that data in the memory card is damaged and so on.
As described above, with the technique disclosed in Japanese Laid-open Patent Publication No. 7-143749, it is possible to notify a digital camera of occurrence of abnormality in power supply. Even if such a technique is applied to a digital camera in which a plurality of power supplies are managed by using communication means of single system, however, an occurrence of power supply abnormality cannot be detected depending on the timing of occurrence of abnormality.